The present invention relates to an apparatus and method for the intravascular ultrasound-guided placement of vena cava filters, said filters often being necessary in the treatment of deep vein thrombosis.
A deep vein thrombosis is a medical condition wherein a blood clot, or thrombus, has formed inside a vein. Such a clot often develops in the calves, legs, or lower abdomen, but occasionally affects other veins in the body. This clot may partially or completely block blood flow, and, unlike clots in superficial veins, the clot may break off and travel through the bloodstream. Commonly, the clot is caused by a pooling of blood in the vein, often when an individual is bed-ridden for an abnormally long duration of time, for example, when resting following surgery or suffering from a debilitating illness, such as a heart attack or traumatic injury.
Deep vein thrombosis of the lower extremities is a serious problem because of the danger that the clot may break off and travel through the bloodstream to the lungs, causing a pulmonary embolism. This is essentially a blockage of the blood supply to the lungs that causes severe hypoxia and cardiac failure. It frequently results in death.
For many patients, anti-coagulant drug therapies may be sufficient to dissipate the clots. For example, patients may be treated with anticoagulants such as heparin and with thrombolytic agents such as streptokinase. Heparin is available and marketed under such trade names as Heparin Lock(trademark), a product of Abbott Laboratories of Abbott Park, Ill.; and Heparin Sodium(trademark), a product of Pharmacia and Upjohn of Peapack, N.J. Streptokinase is available and marketed under such trade names as Streptase(copyright), a product of Behringwerke Aktiengesellschaft of Frankfurt, Germany; and Kabikinase(copyright), a product of Kabivitrum Aktiebolag of Stockholm, Sweden.
Unfortunately, some patients may not respond to such drug therapy or may not tolerate such therapy. For example, patients may have an acute sensitivity to heparin or may suffer from internal bleeding as a result of such drug therapies. Also, such drug therapies simply may be ineffective in preventing recurrent pulmonary emboli. In such circumstances, surgical procedures are required to prevent pulmonary emboli. Methods for prevention of primary or recurrent pulmonary emboli when anticoagulation therapies are ineffective are well-defined in the prior art. The current standard of therapy for prevention of pulmonary emboli in patients who are classified high-risk or are unable to be anticoagulated is percutaneous insertion and placement of an inferior vena cava filter device. A detailed discussion of the construction and use of such filters is contained in U.S. Pat. No. 5,893,869 issued to Barnhart, which is incorporated herein by reference. Additional information on such filters can also be found in an article entitled xe2x80x9cPercutaneous Devices for Vena Cava Filtrationxe2x80x9d by Daniel E. Walsh and Michael Bettmann contained in Current Therapy in Vascular Surgery (3d ed. 1995) at pages 945-949; this article is also incorporated herein by reference.
Placement of these filters is usually accomplished using either the xe2x80x9cfemoral vein approachxe2x80x9d or xe2x80x9cjugular vein approachxe2x80x9d, although alternative approaches, including xe2x80x9caxiliary vein approachesxe2x80x9d, may also be used. There have been a few reports of transabdominal ultrasound being used for placement of filters, but most prior art methods and approaches use fluoroscopy for placement of a guide wire and catheter, as well as for placement and deployment of the filter. Such methods for placement and deployment of a filter also recommend the use of an intravenous dye with contrast angiography.
The fluoroscopy unit may be employed to aid in the placement of the filter in several different ways. For example, the patient is often brought to a operating room or special procedures room, and a fluoroscopy unit is used to identify bony landmarks, allowing the physician to choose the appropriate location for the filter by referencing the bony landmarks. When referencing bony landmarks, placement of the filter is usually done by referencing the lumbar third and fourth vertebrae, making an assumption that the renal veins will be higher than this. However, this method does not provide for an accurate definition of the vena cava size, identification of the position of a clot or thrombus in the vena cava, or accurate identification of the site of the renal veins. It is important to note that, regardless of the method employed in placing the filter, the filter must be placed below the renal veins.
A second and much more accepted method entails the use of a fixed C-arm or fluoroscopic C-arm guidance unit and intravenous contrast in an inferior venacavagram to define the size of the inferior vena cava, to identify the site of the renal veins, and to ascertain the presence or absence of clot at the site proposed for deployment of the filter device. Although this method is often performed in radiology or surgical suites, rather than intensive care units, a general discussion of this method is contained in an article entitled xe2x80x9cPlacement of Inferior Vena Caval Filters in the Intensive Care Unitxe2x80x9d by Drs. Steven C. Rose, Thomas B. Kinney, Karim Valji, and Robert J. Winchell contained in the Journal of Vascular and Interventional Radiology, 8:61-64 (1997); this article is also incorporated herein by reference. Deployment of the filter is then performed per the percutaneous filter placement protocols based on the previously performed venacavagram findings. A distinct disadvantage of this method, however, is that the procedure must be performed in either a special x-ray suite or a specially equipped operating room. Thus, significant expense is involved in carrying out this procedure, especially considering that additional staff is often required for a special suite or an operating room. Moreover, the necessity of this specialized location necessitates the transport of an often critically ill or unstable patient from their hospital room to the site of x-ray equipment.
It is therefore a paramount object of the present invention to provide an apparatus and method for intravascular placement of a filter that does not require the use of cumbersome and specialized fluoroscopy equipment and/or an intravenous contrast.
It is a further object of the present invention to provide an apparatus and method for intravascular placement of a filter that can be performed bedside and thus does not necessitate the movement of the patient.
It is still a further object of the present invention to provide an apparatus and method for intravascular placement of a filter that will substantially reduce the overall time and cost of the placement procedure.
These and other objects and advantages of the present invention will become apparent upon a reading of the following description.
The apparatus of the present invention combines commercially available surgical components into a unitary device for accurate and effective positioning and placement of a vena cava filter. A preferred embodiment of the apparatus of the present invention comprises an outer sheath, an intravascular ultrasound catheter with an ultrasonic imaging element, a guide wire, and the vena cava filter that is to be deployed. The outer sheath, ultrasound catheter, and guide wire share a common central axis. The ultrasound catheter is enclosed by and is moveable relative to the outer sheath, and the guide wire is enclosed by and is moveable relative to the ultrasound catheter. In the stored position, the filter is secured between the outer sheath and the ultrasound catheter.
When the apparatus of the present invention is introduced into a vein, the ultrasound catheter provides real-time imaging of the vein for identifying the appropriate location for placement of the filter. Once such a location has been identified, the outer sheath is drawn back relative to the ultrasound catheter, exposing the legs of the filter, allowing the legs of the filter to spring free and attach themselves to the wall of the vein.
Such an apparatus and the use thereof obviates the need for cumbersome and specialized fluoroscopy equipment and/or an intravenous contrast, while also allowing filter placement to be performed bedside, substantially reducing the overall time and cost of the placement procedure.